I just got 2 x HD 6950's in yesterday and spent the day messing around with them seeing the max hash rate I could get. The cards I got are Gigabyte GV-R6950OC-1GD with 1 GB of RAM. To my disappointment the cards wouldn't unlock and with some research afterwards it turns out the 1 GB models are not unlockable (maybe someone can confirm this for me as well or maybe there is a way I can unlock it and just haven't come across it). So now I thought I'd post here to see what others have done to get the most out of their 6950's.

What I've tried so far:

In Ubuntu 11.04 using SDK 2.4 with poclbm I can get 348 Mhash/s @ 900 Mhz Core and ~1284 Mhz RAM. This is the max I can overclock the card with aticonfig. The original core clock is 870 Mhz so increasing to 900 Mhz isn't really a big difference.

I then tried with Windows 7. I could only get 280 Mhash/s using SDK 2.4 with poclbm and the card at 900 Mhz core and ~1284 Mhz RAM. I'm using the Catalysist version that came with the card. Maybe I need a older version for better hash rate? I tried using Afterburner to clock past 900 Mhz on the core but it would freeze every time.

What puzzles me is I see on the hardware chart on the bitcoin wiki (https://en.bitcoin.it/wiki/Mining_hardware_comparison) that some people have gotten their 6950's past 900 Mhz and some even to 1000 Mhz on the core. I'm not sure why mine won't. Could it be because it's not unlocked or flashed to 6970 BIOS?

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there is no need to push that RAM so high to increase ur mh/s. Install latest display driver + SDK, don't install CCC at all, try phatk kernel. If u want to increase ur GPU Clock u might need to increase the vcore as well, this could be the reason why ur system freezes. Use MSI Afterburner on Windows to OC the card, push GPU to max stable limit, if the limit is reached try to increase the vcore in small steps and push the GPU clock higher, keep an eye on the temps and try to find a stable configuration.

I never overclocked the RAM. I set it as low as it would go. Around 1285 Mhz is the BIOS limit on the RAM. The reason I kept the RAM with Windows 7 the same was to compare the two. I will try lower the RAM in Windows and see if it give me a bit more power to work with.

Ok I just updated to Cat 11.5 and I now get 339 Mhash/s at 900 Mhz processor in Windows 7 Pro. Still not as high as yours but its better. I'm going to try unlocking it again. I tried the way the techpowerups web site says last night and it didn't change the shaders at all. I'm going to try with the other card I have. Maybe its something with the card.